Method for correcting non-uniformity in a rotating tire

ABSTRACT

The method for reducing the radial force variation of a rotating tire by grinding from the tread a portion thereof as determined by the radial motion of a floating load wheel which provides an electrical signal proportional to the movement of the load wheel axis. The electrical signal is employed in a circuit such that when a reference voltage is exceeded, the signal is effective to move a grinder to and away from contact with the tire tread in increments of constant radial depth but of varying time duration. A pulse is synchronized with the tire rotation so each pulse indicates a unit angle of tire rotation. A comparator conducts the pulses only when the signal exceeds a predetermined value such that the pulses activate alternately a pair of one-shot multivibrators which energize actuating solenoids for applying or retracting the grinder. The solenoids move a bell crank which causes a snap-action toggle to advance or retract the grinder with respect to the tire tread.

United States Patent [191 Shively et al.

451 Aug. 28, 1973 METHOD FOR CORRECTING NON-UNIFORMITY IN A ROTATING TIRE {75 l Inventors: Harmon (l. Shively,Tallmadge;

Clifford A. Landsness,Akron, both of Ohio [73] Assignee: The B. F. Goodrich Company,

New York, NY,

[22] Filed: June 15, 1971 [21] Appl. No.: 153,241

Related US. Application Data [62] Division of Ser. No. 849,340, Aug. 12, 1969, Pat. No.

2,766,563 10/1956 Bennett 51/33 R X Primary Examiner-Donald 6. Kelly Attorney-Roger A. Johnston ABSTRACT The method for reducing the radial force variation of a rotating tire by grinding from the tread a portion thereof as determined by the radial motion of a floating load wheel which provides an electrical signal proportional to the movement of the load wheel axis. The electrical signal is employed in a circuit such that when a reference voltage is exceeded, the signal is effective to move a grinder to and away from contact with the tire tread in increments of constant radial depth but of varying time duration. A pulse is synchronized with the tire rotation so each pulse indicates a unit angle of tire rotation. A comparator conducts the pulses only when the signal exceeds a predetermined value such that the pulses activate alternately a pair of one-shot multivibrators which energize actuating solenoids for applying or retracting the grinder. The solenoids move a bell crank which causes a snap-action toggle to advance or retract the grinder with respect to the tire tread.

6 Claims, 5 Drawing Figures Patented Aug. 28, 1973 4 Sheets-Sheet 1 mm Wm WM @N mm INVENTORS HARMON G. SHIVELY CL 0 CLIFFORD A.LANnsNEss Patented Aug. 28, 1973 3,754,358

4 Sheets-Sheet 2 FIG. 3

INVENTORS HARMON G. SHIVELY CLIFFORD A. LANDSNESS ATTI.

Patented Aug. 28, 1973 3,754,358

4 Sheets-Sheet .3

I" I W SENSOR f/ja /4 AMPLIFIER 1 PULSE oNE PULSE/DEG.

GATE [5- REFERENCE [6 VOLTAGE. PULSER COMPARATOR 18 l7 AMPLIFIER Mi "jGRlND" I IIIIIII IIIIIIII I R 6 DELAY No GRIND" (SHIFT "\19 REGISTER) 30 AMPLIFIER 2] POWER SUPPLY TRIGGER -32 33 FIG. 46.. so MILL|SEC. INTEGRATING DELAY START Q l l O 6 R I\.ID" IIIIIIIIIII E INVENTORS HAR MON 6. ISHIVELY CLIFFORD A. LANDSNESS E WAW Patented Aug. 28, 1973 4 Sheets-Sheet 4 ONE SHOT (DECAYING VOLTAGE) MULTl-VlBRATOR {START No GRIND" ONE SHOT MULTl-VIBRATOR (Rssms VOLTAGE) 8OMILLI- GOMILLI- SEQOELAY 30 MILLI SEO.DELAY NO-GRIND" SOLENOID GRIND" SOLENOID BELL CRANK GRINDER INVENTORS {START "GRIND" HARMON G. SHIVELY LIF'FORD A. LANDSNESS BY wam METHOD FOR CORRECTING NON-UNIFORMKTY IN A ROTATING TIRE CROSS-REFERENCE TO RELATED APPLICATIONS This application is a division of our copending application Ser. No. 849,340 filed Aug. 12, 1969 entitled Apparatus for Correcting Non-Uniformity in a Rotating Tire, issued Aug. 8, 1972 as U.S. Pat. No. 3,681,877.

BACKGROUND OF THE INVENTION It is essential that pneumatic tires for vehicles, such as passenger automobiles, exert a minimum force variation on the axle while running under load in order to prevent undesirable oscillations of the vehicle suspension. Therefore, the dynamic variation in the forces radially applied to the axle while the tire is rotating must be kept to a minimum in order to produce this result. When the allowable limits of radial force variation of the completed tire are exceeded, the tire is generally unusable for passenger car service. This requires that the pneumatic tires be manufactured or corrected to maintain within predetermined limits the eccentricity or radial runout, carcass flex-stiffness and lateral oscillation. One method of reducing the radial force variation of a completed tire is that of buffing or grinding rubber from the tread region of the tire, preferably from the axial edges thereof.

In the manufacture of pneumatic tires, one common means of determining the radial force variation of a completed tire is that of testing the tire on a uniformity machine. In this type machine, the tire is mounted on a rim and in the inflated state is rotated at a nearly constant speed. A movable load wheel is urged into contact with the tread of the tire while it is rotating. The load wheel has sensors, usually electrical transducers, attached to its shaft, or axle mounting, such that motion of the load wheel is detected in a direction radial to the tire and an electrical signal varying proportionally to the load wheel movement is provided. The varying voltage of the electrical signal corresponds to the variation in radial force of the tire tread against the load wheel since the movement of the load wheel is directly proportional to the variations in radial force exerted by the tire on the load wheel.

In order to reduce the radial force variation by re moving material from the tread region while the tire is rotating on a uniformity machine, it is necessary to apply the varying electrical signal from the load wheel transducers to a controlling and actuating mechanism for operating the material remover which may be a buffer, or grinder, as the case may be. A convenient technique of providing grinder of buffer operation has been to drive the grinder at a fixed rotational speed and alternately move the grinding wheel into contact with the tire tread and then away from the tread.

Heretofore, in order to control the amount of material removed from the tire tread region by the grinder, attempts have been made to control the radial depth of penetration of the grinder in the tire tread by making the radial movement of the grinder proportional to the voltage of the electrical signal emanating from the load wheel transducers. This type of grinder control is often called a linear" system in view of the attempts to make the grinder movement directly proportional to the magnitude of voltage of the continuously varying electrical signal.

In practice, the linear type of grinder control is extremely difficult to achieve in order to remove enough material from the tire tread at the proper peripheral location on the tire when the tire is rotating at even mod est speeds. The problem is due primarily to the difficulty in moving the large mass of the grinder alternately radially inwardly and outwardly at sufficient speed to provide the required grinder responsiveness to the variation in the electrical signal voltage at the frequency produced by the tire rotational speed. This difficulty has served to render an otherwise useful method of salvaging defective tires impractical in view of the complexity and cost of machinery necessary to provide adequate grinder response movement.

Heretofore, a grinder capable of removing material rapidly enough to enable grinding at typical tire uniformity test rotation speeds exhibited such a large mass that the actuators and controls, for providing the force required to move the grinder quickly enough to grind only at the proper tire location, did not have sufficient sensitivity to respond to the frequency of the signal from the load wheel sensors. Thus, the method of grinding tire treads to reduce variation in tire radial force to acceptable limits for use in passenger vehicle production has required grinding equipment of great complexity and prohibitive cost.

SUMMARY OF THE INVENTION The present invention provides a solution to the problem of removing material from the tread region of a rotating tire by moving the grinder radially into and away from contact with the tire tread in increments of constant radial depth but of varying time duration. The varying electrical signal from the load wheel sensors of a uniformity testing apparatus is compared with a fixed reference voltage level representing the maximum allowable variation in radial force and is conducted only when the voltage exceeds the reference level. A series of equal electrical pulses, each representing a unit angle of tire rotation is provided by a generator on the rotating tire axle and these pulses are permitted to be conducted only when the signal from the load wheel sensors exceeds the reference level. The pulses are applied to a pair of single pulse generators which alternately energize actuators for moving a grinder either into contact or away from the tire tread. The actuators are interconnected to a snap-action, spring loaded toggle which is set close to the trip point such that only a small force from either actuator is required to trip the toggle which moves the grinder a fixed radial distance either into contact with or away from the tire tread.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view of a tire uniformity machine incorporating the present invention in its preferred embodiment;

FIG. 2 is a plan view of the grinder and actuator portion of FIG. 1;

FIG. 3 is a portion of a sectional view taken along the section indicating lines 3-3 of FIG. 2; and

FIG. 4a and 4b, when placed in vertical alignment, comprise a block flow diagram of the control circuit for operating the grinder.

DETAILED DESCRIPTION Referring now to FIG. 1, a tire uniformity machine M is shown in side view having a tire T mounted therein on a vertically disposed axle arrangement which, in the usual practice, comprises two movable rotatable chuck plates 10a and 10b such that the tire may be mounted, inflated and rotated about a vertical shaft 10. A load wheel W is positioned such that it may be moved radially into contact with the tread of the tire. The load wheel is supported by bearings 12 at the ends of the vertical shaft 10 and the bearings are resiliently mounted on flex plates 1 1 such that the load wheel can move in its plane of rotation in a direction perpendicular to its axle 10'. Sensors 1 la are mounted on the flex plates 11 for determining the motion of the load wheel axle. In the preferred practice of the invention, the sensors 11a comprise electrical transducers which provide a varying electrical signal with the magnitude of the signal voltage directly proportional to the radial displacement of the loadwheel axle 10'. The tire T is rotated by a power means P connected to its axle l and mounting chucks a and 10b of the tire.

The load wheel and its axle 10' and bearing assembly are mounted on a movable carriage C which is slidably mounted on rails R to urge the load wheel W into contact with the tire tread. The load wheel is shown in the retracted position in FIG. 1 with the surface of the wheel not contacting the tire tread. A threaded power nut N is engaged with a threaded jack screw S attached to the carriage C and the threaded nut is rotated by a motor and transmission assembly P. Rotation of the nut N causes the load wheel to be brought to and from contact with the tire tread. The arrangement of the tire uniformity machine in FIG. 1 may be essentially as described in US. Pat. No. 3,500,681 issued Mar. 17, 1970, entitled LOCATING MAXIMUM RADIAL FORCE VARIATION IN A TIRE, in which patent is disclosed and claimed the machine and its operation for providing an electrical signal for indicating force variation in the tire.

Referring now to FIGS. 2 and 3, the detail of the grinder mechanism are shown enlarged from FIG. 1 such that the description thereof may be more clearly understood. The grinder G is rotatably mounted on a lever 40 intermediate the ends thereof and a second lever 41 has one end pivotally attached to lever 40 at the point where the grinder G is mounted thereon. Levers 40 and 41 intersect and are pivotally attached such that each may be moved with respect to the other with the grinder G being free to rotate and unaffected in its rotation by the scissor-like movement of either lever 40 or 41.

One end of the lever 40 has a register means 42 attached thereto for making contact with the tire tread. Similarly, the lever 41 has a portion 41a intermediate the ends thereof which portion has a second register means 43 attached thereto for making running contact with the tire tread. In the preferred form of the invention, the register means 42 and 43 comprises a pair of spaced idler rollers rotatably mounted respectively to levers 40 and 41. The rollers 42 and 43 are spaced closely adjacent on opposite sides of the grinder with the axis of rotation of each idler parallel to that of the grinder. In operation, scissoring the levers 40 and 41 moves the idlers toward or away from each other, thereby advancing or retracting the grinder G radially with respect to its position in relation to the tire tread. Levers 40 and 41 are scissored such that when the idler rollers 42 and 43 are advanced toward the center of the rotating tire: the grinder G is thus retracted from grind position. When the levers 40 and 41 are scissored such that the idlers 42 and 43 are retracted away from the center of the tire, the grinder G is advanced toward and urged into contact with the tire tread for removing material therefrom.

The grinder and actuator assembly is supported by an elongated bar 44, see FIG. 2, having one end 44b pivotally attached to the intersection of lever-arms 40 and 41 and the other end of the bar 44 pivotally attached to a frame means 45 at a pivot mount 45a provided thereon for connecting to the said bar. The frame means comprises a portion of the frame of the machine shown in FIG. 1. The bar 44 has a mounting portion 44c intermediate the ends thereof with a clevis 46 pivotally attached thereto, which clevis is interconnected to an actuator 47 having one operative portion thereof pivotally connected to a second mounting portion 45b spaced from the pivot mount portion 45a on said frame. In the preferred practice of the invention, the actuator 47 comprises a pneumatic or hydraulic power cylinder with one end connected to clevis 46 and the other end pivotally attached to the frame 45. In operation, power cylinder 47 operates to rotate the arm 44 about the first mount portion 45a of the frame such that the entire grinder assembly is moved toward or away from the rotating tire. The power cylinder 47 is operated to urge the grinder and idler rollers 42 and 43 into contact with the tire tread, it being determined by the scissored position of the levers 40 and 41 with respect to each other whether or not the grinder contacts the tire. However, the idler rollers 42 and 43 are preferably positioned such that initially the rollers engage the tire tread, the grinder G remaining spaced from the tire tread.

A pulley 48 is provided on the shaft of the grinder G and is operatively interconnected by means of a driving belt 49 to a power means 50 rigidly attached to frame 45. In the presently preferred practice, power means 50 is a motor having its shaft of rotation axially coincident with the center of pivot of the end 44a of the bar 44. This permits the arm 44 to be rotated about its pivotal attachment to the frame without changing the distance between the pulley 48 and the shaft of the motor, thus maintaining constant tension in the drive belt 49 in all positions of the arm 44.

The free end of the lever 40 has a clevis 40a attached thereon. The free end of the lever 41 has a fork 41 rigidly forrned therein with the arms of the fork extending from the lever 41 in spaced mutually parallel arrangement with each arm of fork 41' parallel to the length of the arm 41. Between the arms of the fork 41 is a bell crank 30 having rigidly mounted, intermediate its ends, a rigid pivot shaft 300 extending perpendicularly from the bell crank. The ends 30b of the shaft are rotatably mounted in the arms of the fork 41 such that the pivot shaft 300 is parallel to the axis of rotation of the grinder. The bell crank 30 also has a portion 300, see FIG. 3, extending therefrom, which portion has one end of a linkage bar 52 pivotally attached thereto and the other end of the linkage bar pivotally attached to the clevis 40a on the end of the arm member 40. In operation, rotation of the bell crank about its shaft 30a causes the linkage bar 52 to operate as a toggle for scissoring the ends of the arm members 40 and 41 with respect to each other. As described above, this movement then causes the idler rollers 42 and 43 to move together or further apart, thereby extending or retracting the grinder respectively away from or towards the center of the tire.

A U-shaped bracket 53, having each of its open ends adjustably attached to one end respectively of the fork 41', see FIGS. 2 and 3, has mounted in the closed portion thereof actuator means 26 and 27 for rotating the bell crank. As described above with reference to FIG. 4a and 4b, the actuator means comprise respectively a pair of electrical solenoids 26 and 27. Each solenoid has respectively an armature 26a and 27a extending therefrom with each armature having respectively a clevix 26b and 27b attached to the end thereof. The clevis 26b is attached to one arm of the bell crank 30 such that, upon electrical energizing, the solenoid 26 causes the armature 26a to retract, thereby rotating the bell crank in a direction such that the bar 52 causes lever-arms 40 and 41 to scissor with respect to each other in a manner spreading the idler rollers 42 and 43 further apart and permitting the grinder G to contact the tire. The clevis 27b is pivotally attached to an arm of the bell crank on the opposite side of the pivot shaft 30a from the clevis 26b. In operation, electrical actuation of solenoid 27 causes the armature 27a to retract, thus rotating the bell crank 30 in a direction such that the linkage 52 scissors lever arm members 40 and 41 in a manner converging idler rollers 42 and 43 toward each other thereby retracting the grinder G from material removing position.

Thus, the grinder G is advanced toward or retracted away from material-removing, or grinding, position by alternate actuation of the solenoids 26 and 27. The limitations of the actuating stroke of the solenoids thus determine the limit of radial travel of the grinder. The grinder thus operates in a succession of predetermined fixed radial movements toward or away from the tire, with each movement providing the same depth of penetration of the grinder into the tire tread as the previous movement.

A snap-action means indicated by arrow F in FIG. 2 and FIG. 3 is provided to assist the toggle action of the bell crank 30 and the linkage bar 52 such that in the retracted or no grind position, the snap-action mechanism F is near the trip point. A small amount of movement of the armature 26a of the grind solenoid causes the snap-action mechanism F to go over center and provide a continuing force assist to movement of the bell crank 30. In the grind" position the snapaction means is near the trip point for the return stroke such that a small amount of movement of the armature 27a of the no grind" solenoid 27 causes the snapaction means to throw over center and give force assistance to the retracting stroke of the bell crank 30.

In the preferred form of the invention, the snapaction means F comprises a generally tr-shaped frame 54 having the open ends of the sides thereof adjustably attached to the sides of bracket 53. A connecting bar 55 extends through the pivotal connection between the linkage bar 52 and the arm 300 of the bell crank and also extends through clearance holes 53a formed one in each side of the bracket 53 such that movement of the bell crank causes the bar 55 to move laterally within the clearance holes 53a. A pair of coil springs 56 and 57 is provided with the end of one spring attached each to one end of the bar 55 and the opposite end of the coil spring anchored to an extension of the closed end of the bracket 54. The springs are disposed such that snap-action occurs about a line through the pivot center of the bell crank passing through the end of the coil spring anchored to the bracket 54. The springs are thus positioned in mutually parallel arrangement and provide a snap-action of the bell crank 30 about its pivot axis. An adjustment means 58 is provided at the attachment of the bracket 54 to the bracket 53 such that the position of the coil springs may be changed for effecting a snap-action pivoting of the bell crank at a different position in its rotation. In the preferred form of the invention, the adjustment is provided by a slot 54a in each side of bracket 54 and a threaded bolt 58 attached respectively to each side of the bracket 53. The bracket 54 is pivotally mounted about the pivot center of the bell crank and it is attached to bracket 53 such that the attachment bolts 58 may be loosened and bracket 54 pivoted about the bell crank pivot center and the bolts 58 then tightened to secure the new position of the bracket 54 with respect to bracket 53 thus permitting variation in the snap position of the bell crank.

A further adjustment in the mechanism is provided by a sleeve nut 52a attached to the linkage bar 52 such that the bar may be lengthened or shortened by rotation of the sleeve nut. This permits changes in the relative positions of the arms 40 and 41 with respect to each other such that the idler wheels 42 and 43 may be adjusted with respect to the grinder G.

In operation, the power cylinder 47 is actuated by an independent source to move arm 44 to bring the idler rollers 42 and 43 into running contact with the rotating tire T when it is desired to begin the material-removing cycle. The motor 50 may then be started to bring the grinder wheel G to the desired rotational speed.

Referring now to FIG. 4a and 4b, a schematic flow diagram is shown in which the signal from the sensors 11a is fed to amplifier M and then to a pulse-gate IS. A pulse generating means, or pulser, 16 (see also FIG. 1) is driven by the tire axle 10 such that rotation of the tire mounted thereon causes the pulse generator to transmit equal pulses with each pulse representing a unit angle of tire rotation. In the preferred practice of the invention, the pulse generator 16, or pulser, as it is labeled in FlG. 4a, has an output signal of one pulse per degree of tire rotation, which output is applied to the input of the pulse-gate. The pulser 16 may be of any convenient commercial type. In the present practice of the invention, a Rotaswitch Pulser, Model No. 815- P3431, manufactured by the Disc Instrument Company, has been used, but any other commercially available unit may be employed. Similarly, the pulse-gate 15 may be of any standard construction or type known in the art and it may be of semi-conductor or vacuumtube design. Operation of the pulse-gate 15 is such that the signals from the amplifier 14 are not transmitted by the pulse-gate unless the pulse-gate 15 is receiving pulses from the generator 16.

The signals passed from the pulse-gate R5 are then applied to a comparator amplifier 18 which receives also a voltage from a reference source 17. The comparator amplifier 18 operates as a summing amplifier such that the pulses are transmitted to its output only when the voltage signal from the sensors exceeds the level from the reference source 17. The reference voltage is a predetermined value to represent the maximum allowable limit of radial force variation which is permissible in the tire. When the signal from the sensors exceeds this level in magnitude, the pulses from the generator 16 are transmitted and used to initiate the grinder operation.

Signals from the comparator amplifier 18 are applied to the input of a delay means 19 which serves to delay the signal an amount in tire rotation time represented by the angular distance the tire must rotate for a point under the load wheel to pass under a grinder G. This angular distance is represented in the upper right-hand portion of FIG. 4a by the Greek letter Theta 0. The grinder G is located at a convenient position around the tire and delay means 19 is used to synchronize operation of the grinder with passage of the point associated with a high radial force value, such that the grinder G does not operate until the point passes in rotation directly beneath the grinder.

The delay means 19 preferably comprises a static shift register which may be of conventional design known in the art and may be of vacuum-tube or semiconductor design or may employ relays. In the presently preferred practice the shift register is a Motorola static eight-bit shift register, Model MC845P. The pulse signals from the shift register are applied to a second amplifier 20 and subsequently applied to an electrical trigger 22 which is supplied power from the power supply 21. The trigger 22 serves to apply sufficient power to means for moving the grinder toward and away from the tire tread. The trigger 22 may be of any conventional construction known in the electrical art. In the preferred practice of the invention, a silicon control rectifier (SCR) firing circuit is employed with the signal from amplifier 20 applied to the gate junction of the SCR. The signal from the trigger is then applied to the grinder moving means through an intermediate integrating delay 23 and simultaneous application to a pair of intermediate single pulse generators 24 and 25.

The integrating delay 23 is preferably a 30 millisecond delay to prevent activation of either multivibrator upon receipt of a series of pulse signals of a duration less than 30 milliseconds. However, any convenient time value may be used for the delay 23, the choice being governed by the mechanical time response of the grinder mechanism in moving toward and away from the tire tread. The single pulse generators 24 and 25 are preferably one-shot multi-vibrators with the generator 24 operating only upon excitation by the decaying voltage portion of the pulse signal, the generator 25 being energized only upon receipt of the rising voltage portion of the pulse signal. The output of the multivibrator 24 is applied to an actuator 27 which retracts the grinder G from contact with the tire tread and the output of multivibrator 25 is applied to an actuator 26 which moves the grinder G to contact the tire tread. In the presently preferred practice of the invention, the actuators 26 and 27 each comprise an electrical solenoid having an armature therein with one end of each armature connected to bell crank 30 which in turn is connected to the grinder G.

In operation, when a signal from the multivibrator 25 is received, by the rising voltage of the first pulse in each group of pulses applied to the multivibrator, the solenoid 26 is activated, which causes the bell crank to move the grinder into material-grinding position. As the group of pulse passes, application of the decaying voltage portion of the last pulse in the group to multivibrator 24 causes the solenoid 27 to be activated, which in turn rotates the bell crank in the opposite direction, thereby retracting the grinder from material-grinding position.

The design of each of the multivibrators 24 and 25 is such that the pulse width of the output signal is greater than the time response of the grinder activating mechanism to prevent signals, which have a time duration less than the response capability of the solenoid activating device, from being applied to the solenoid. It will be readily apparent that such an arrangement is necessary to prevent chatter of the solenoid actuating mechanism.

The output of multivibrator 25 is also applied to a 30 millisecond delay 28 and the output thereof is fed back into the input of the decaying-voltage sensitive multivibrator 24. Similarly, the output of multivibrator 24 is applied also to a 30 millisecond delay 29 the output of which is fed back into the input of the multivibrator 25. This arrangement provides a cross-coupled delay feedback of the multivibrator outputs and in operation serves to prevent either multivibrator from activating for a period of time equal to the pulse width of the output of the multivibrators.

In FIG. 4b, the multivibrator 25 and solenoid 26 which cause the grinder to move into contact with the tire are labeled as a grind function and the multivibrator 24 and solenoid 27 for retracting the grinder from material grinding position are labeled as the no grind function. Referring, in FIG. 4a, to the electrical output of comparator amplifier 18, the maximum voltage of the pulse signals therefrom represents a grind signal and the zero voltage level between pulse groups represents the no grind portion of the signal. With respect to the signal applied to the input of the multivibrators, the rising voltage side of the pulse group represents the start grind function and the decaying voltage side of the pulse group represents the start nogrind" function.

Upon receipt of electrical pulse signal from the one shot multivibrator 25 the grind solenoid 26 is actuated to rotate the bell crank, thereby scissoring lever arms 40 and 41 such that the idler rollers 42,43 are moved farther apart and the rotating grinder G is moved a predetermined distance into contact with the tire tread for removing'material in the tread region. When an electrical pulse signal is received from the one-shot multivibrator 24 by the no-grind solenoid 26, the armature of the solenoid is actuated to rotate the bell crank 30 in a direction such that the lever arms 40,41 are scissored and the idler rollers 42,43 are moved closer together thereby retracting the grinder G from material removing position. Thus, alternate actuation of the grind" solenoid 26 and the no grind solenoid 27 provides movement of the rotating grinder G a predetermined distance into and away from the material-removing position. Springs 56 and 57 provide a snap-action force assist to rotation of the bell crank. Upon completion of the grinding cycle, eg when the magnitude of signals from sensor are no longer in excess of the reference voltage for the predetermined minimum time duration, the power cylinder 47 is actuated to pivot arm 44 and move the grinder assembly out of material-removing position, in a direction radially outward of the tire, such that the idler rollers no longer run against the rotating tire.

The method of the present invention thus incorporates the use of separate actuators for moving the grinder a predetermined and fixed distance into contact with, and away from, the tire tread upon receipt of a grind" or a no grind" signal to the respective actuators. This technique is in contrast to one commonly known system wherein attempts have been made to mechanically actuate the grinders to move a distance into contact and away from the tire directly proportional to the continuing variation in the voltage from the radial force measuring sensors. The grinder in the present invention thus is urged into contact with the tire, grinds for a time determined by the pulse width of an electrical grind" signal and then is retracted from the grind position until receipt of another grind signal.

Modifications and adaptations of the invention may be made by those having ordinary skill in the art with the invention being more particularly defined by the following claims.

We claim:

1. The method of reducing the magnitude of radial force variation in a pneumatic tire comprising:

a. inflating the tire and rotating it about its axis;

b. providing an electrical signal, the amplitude and duration of which is representative of the radial force variation of the rotating tire;

c. engaging the tread of the rotating tire to a predetermined depth under a force independent of force variations in said tire and in the locality productive of said signal with a means for removing rubber from the tread region in response to said signal;

(1. continuing the engagement of the materialremov'mg means for that portion of a single revolution of the tire corresponding to the time in which said signal is in excess of a predetermined minimum; and,

e. continuing rotation of the tire and operation of said material-removing means until the maximum radial force variation signal does not exceed said predetermined minimum.

2. The method defined in claim 1 further comprising the steps of:

a. providing a reference signal the voltage of which is representative of the said predetermined minimum of radial force variation;

b. comparing said electrical signal with said reference signal; and

c. permitting said electrical signal to be conducted only when same is greater in value than said reference signal.

3. The method defined in claim 1, further comprising the steps of:

a. providing a series of equal duration direct current pulses which pulses are synchronized with the rotation of said tire such that each pulse represents a unit angle of tire rotation;

b. providing an electrical gating means and applying said pulses and said electrical signal to the input of said gating means such that said electrical signal is passed only when said pulses are received by said gating means.

4. The method defined in claim 3 wherein:

a. movement of said material-removing means into engagement with said tire is initiated by the first of said series of pulses; and

b. movement of the material-removing means away from material-removing position is initiated by the last of said series of pulses.

5. The method defined in claim I, further comprising preventing engagement of the tire with said means for removing material from the tread region until the amplitude of said electrical signal is in excess of a predetermined minimum and the duration exceeds a predetermined minimum time.

6. The method defined in claim 5 wherein said predetermined minimum duration is 30 millisecondsv =& a: =9 

1. The method of reducing the magnitude of radial force variation in a pneumatic tire comprising: a. inflating the tire and rotating it about its axis; b. providing an electrical signal, the amplitude and duration of which is representative of the radial force variation of the rotating tire; c. engaging the tread of the rotating tire to a predetermined depth under a force independent of force variations in said tire and in the locality productive of said signal with a means for removing rubber from the tread region in response to said signal; d. continuing the engagement of the material-removing means for that portion of a single revolution of the tire corresponding to the time in which said signal is in excess of a predetermined minimum; and, e. continuing rotation of the tire and operation of said material-removing means until the maximum radial force variation signal does not exceed said predetermined minimum.
 2. The method defined in claim 1 further comprising the steps of: a. providing a reference signal the voltage of which is representative of the said predetermined minimum of radial force variation; b. comparing said electrical signal with said referenCe signal; and c. permitting said electrical signal to be conducted only when same is greater in value than said reference signal.
 3. The method defined in claim 1, further comprising the steps of: a. providing a series of equal duration direct current pulses which pulses are synchronized with the rotation of said tire such that each pulse represents a unit angle of tire rotation; b. providing an electrical gating means and applying said pulses and said electrical signal to the input of said gating means such that said electrical signal is passed only when said pulses are received by said gating means.
 4. The method defined in claim 3 wherein: a. movement of said material-removing means into engagement with said tire is initiated by the first of said series of pulses; and b. movement of the material-removing means away from material-removing position is initiated by the last of said series of pulses.
 5. The method defined in claim 1, further comprising preventing engagement of the tire with said means for removing material from the tread region until the amplitude of said electrical signal is in excess of a predetermined minimum and the duration exceeds a predetermined minimum time.
 6. The method defined in claim 5 wherein said predetermined minimum duration is 30 milliseconds. 